1. Field of Invention
The invention relates to a gear drive mechanism that drives a drive shaft in an office product. In particular, the gear drive mechanism is provided with a gear removal preventive (i.e. a lock) after a gear is fit to a cantilever-like shaft.
2. Description of Related Art
As a conventional office product, label writers have been used to print characters and the like on a label tape. A cassette in which the label tape is wound is installed in the label writer. The label writer feeds the label tape from the cassette to a printhead. A printhead prints characters and the like on the label tape and a platen roller discharges the printed label tape outside a main body using a nip roller. Such a series of driving in the label writer is performed by a gear drive mechanism provided in the main body of the label writer under the cassette.
The gear drive mechanism is structured such that a plurality of shafts, including a drive shaft, cantilevers from a base plate. Gears are fit into the respective shafts, with the gears engaged with each other such that the gears are prevented from coming off of the shafts. A general method for preventing the gears from coming off includes a groove formed around an end of the shaft with a removal preventive washer fit into the groove.
In the conventional drive mechanism, an E-shaped removal preventive clip, that is an elastic metal plate, is used for the removal preventive washer. The E-shaped removal preventive clip is shaped like the letter C having a protrusion at the center. The E-shaped removal preventive clip has an opening with respect to the shaft, so that the E-shaped removal preventive clip can be easily attached/detached to/from the shaft.
However, the size, thickness, material and shape of the E-shaped removal preventive clip are specified in the JIS Standard. Thus, the size variety of the E-shaped removal preventive clip is small. Therefore, in the conventional gear drive mechanism, the diameter and length of the shaft has been determined based on the specifications of the E-shaped removal preventive clip. Small office products, such as the label writer, requires that the gear drive mechanism to be slim and lightweight. However, in creating the slim and lightweight gear drive mechanism, the gear drive mechanism is limited to the specifications of the E-shaped removal preventive clip. If the specified E-shaped removal preventive clip is not used, it becomes possible to slim the gear drive mechanism and lower its weight. However, it is difficult to disassemble the gear drive mechanism.
The invention provides a gear drive mechanism that is easy to disassemble and contributes to the miniaturization of the office products by thinning the gear drive mechanism.
In various exemplary aspects of a gear drive mechanism that drives a specific shaft by which a plurality of shafts cantilever from a base plate, wherein gears are fit to the shafts and engaged with each other, the gear drive mechanism includes a groove formed around an end of at least one of the shafts other than the specific shaft, a washer having a ring-shape and a slit in a direction of a diameter fit in the groove as a gear removal preventive of the gear and a recessed portion provided in a part of a side surface of the gear throughout the washer.
According to the gear drive mechanism of this invention, the gear can be prevented from coming off by using the thin ring-shaped washer having a simple structure and the slit in the direction of diameter. Because the washer has the simple structure, a diameter and length of the shaft can be minimized using the washer conforming to the shaft. Further, the gear drive mechanism can be easily disassembled by which the slit in the washer is aligned with the recessed portion provided to the side surface of the gear, with a tool inserted in the recessed portion. Furthermore, the gear drive mechanism can be thin, so that the office products can be downsized.